# The effect of the stochasticity of photoionization on 3D streamer simulations

## TL;DR

This study investigates how stochastic fluctuations in photoionization influence the behavior and morphology of positive streamers in air, revealing that fluctuations can affect streamer stability and branching.

## Contribution

It introduces a comparison between stochastic and continuum photoionization models in 3D streamer simulations, highlighting the impact of photoionization variability on streamer dynamics.

## Key findings

- Stochastic fluctuations cause variations in streamer properties.
- Results with stochastic and continuum models agree when photoionization is high.
- Reduced photoionization increases stochastic effects and streamer branching.

## Abstract

Positive streamer discharges require a source of free electrons ahead of them for their growth. In air, these electrons are typically provided by photoionization. Here we investigate how stochastic fluctuations due to the discreteness of ionizing photons affect positive streamers in air. We simulate positive streamers between two planar electrodes with a 3D plasma fluid model, using both a stochastic and a continuum method for photoionization. With stochastic photoionization, fluctuations are visible in the streamer's direction, maximal electric field, velocity, and electron density. The streamers do not branch, and we find good agreement between the averaged stochastic results and the results with continuum photoionization. The streamers stay roughly axisymmetric, and we show that results obtained with an axisymmetric model indeed agree well with the 3D results. However, we find that positive streamers are sensitive to the amount of photoionization. When the amount of photoionization is doubled, there is even better agreement between the stochastic and continuum results, but with half the amount of photoionization, stochastic fluctuations become more important and streamer branching starts to occur.